Of 10 patients with fatal coronary heart disease undergoing coronary angiography 0-69 days (average 21) before necropsy, the amount of narrowing in 61 coronary arteries observed angiographically (diameter reduction) during life by three angiographers was compared to that observed histologically (cross-sectional area) at necrospsy. Of 11 coronary arteries or their subdivisions narrowed 0-50% in cross-sectional area histologically, none were underestimated angiographically; of eight narrowed 51-75% histologically, seven had been underestimated, and of 42 narrowed 76-100% histologically, 17 (40%) were underestimated angiographically.